Hydroxyl Group

4 Key excerpts on "Hydroxyl Group"

• 

  eBook - ePub

  Principles of Organic Chemistry

  • Robert J. Ouellette, J. David Rawn(Authors)
  • 2015(Publication Date)
  • Elsevier

    (Publisher)

  8

  Alcohols and Phenols

  8.1 The Hydroxyl Group

  Families of organic compounds that have functional groups containing oxygen include alcohols, phenols, ethers, aldehydes, ketones, acids, esters, and amides. Alcohols and phenols both contain a Hydroxyl Group (–OH). A Hydroxyl Group is also present in carboxylic acids, but it is bonded to a carbonyl carbon atom. As a result, the chemistry of carboxylic acids, the subject of Chapter 12 , is substantially different from the chemistry of alcohols and phenols. Alcohols and phenols can be viewed as organic “relatives” of water in which one hydrogen atom is replaced by an alkyl group or an aryl group. Alcohols contain a Hydroxyl Group bonded to an sp3 -hybridized carbon atom. Phenols have a Hydroxyl Group bonded to an sp2 -hybridized carbon atom of an aromatic ring.

  Common Names of Alcohols

  The common names of alcohols consist of the name of the alkyl group (Section 3.3 ) followed by the term alcohol . For example, CH3 CH2 OH is ethyl alcohol and CH3 CH(OH)CH3 is isopropyl alcohol. Other common names are allyl alcohol and benzyl alcohol, whose structures are shown below.

  The IUPAC system of naming alcohols is based on the longest chain of carbon atoms that includes the Hydroxyl Group as the parent chain. The parent name is obtained by substituting the suffix -ol for the final -e of the corresponding alkane. The IUPAC rules are as follows:

  1.  

  The position of the Hydroxyl Group is indicated by the number of the carbon atom to which it is attached. The chain is numbered so that the carbon atom bearing the Hydroxyl Group has the lower number.

  The longest chain that contains the Hydroxyl Group has 4 carbon atoms. An OH group is at C-2 and a methyl group is at C-3. So, the name is 3-methyl-2-butanol

  2.  

  When the Hydroxyl Group is attached to a ring, the ring is numbered starting with the carbon atom bearing the Hydroxyl Group. Numbering continues in the direction that gives the lowest numbers to carbon atoms with substituents such as alkyl groups. The number 1 is not used in the name to indicate the position of the Hydroxyl Group.

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  eBook - ePub

  Pharmaceutical Chemistry E-Book

  • David G. Watson(Author)
  • 2011(Publication Date)
  • Churchill Livingstone

    (Publisher)

  Chapter 5 Oxygen- and sulphur-containing functional groups

  David G. Watson

  Chapter contents

  Introduction 77

  Monohydric alcohols 78

  Ethanol 78

  Other aliphatic alcohols 79

  Benzyl alcohol 79

  Diols and triols 79

  Polyols 80

  Some chemical properties of alcohols 81

  Loss of water 81

  Oxidation 81

  Phenols 81

  Esterification 86

  Ethers 88

  Aldehydes and ketones 89

  Carboxylic acids 91

  Salts of carboxylic acids 93

  Salts formed between amines and carboxylic acids 94

  Esters 94

  Chemical stability 95

  Enzymatic hydrolysis of esters 97

  The role of esters in modifying physicochemical properties of drugs 101

  Esters for improving drug absorption 101

  Esters for improving water solubility 102

  Esters used for sustained drug delivery 103

  Esters for improving drug acceptability and reducing side effects 103

  The role of esters in terminating drug action 105

  Participation of the ester group in drug action 105

  The ester linkage in polymeric drugs 107

  Esters in biological systems 108

  Phosphate esters in biology 108

  Introduction

  Oxygen in the most electronegative element found in biomolecules since fluorine does not occur naturally in biological compounds. Its high affinity for electrons means that unlike nitrogen it does not share its lone pairs with protons readily. Thus oxygen-containing groups tend to be less potent in conferring pharmacological activity. For example, dopamine differs from noradrenaline by lacking a Hydroxyl Group but they both have potent effects on the heart: remove the amine group and activity is totally abolished. This is really a generalisation, it is probably truer to say that where oxygen-containing groups play an important role in conferring pharmacological activity they have a very specifically targeted function. In contrast, the charged nitrogen atom exerts a more general effect and may affect a number of targets. This theme will be expanded later in the chapter. Water is the fundamental oxygen-containing biologically active substance and some of its unique properties have been discussed in Chapter 1

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  eBook - ePub

  Biochemistry

  An Organic Chemistry Approach

  • Michael B. Smith(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  Any atom other than carbon or hydrogen (e.g., oxygen, nitrogen, sulfur, chlorine, etc.) is called a heteroatom. These heteroatoms are more electronegative than carbon or hydrogen, and the heteroatom will impart bond polarization to any single or multiple bond (C—X or C=X) in the molecule. Such molecules are considered to be polar. The valence of the heteroatom will determine how many atoms are attached to that heteroatom. Oxygen has a valence of 2 and must form X—O—X or C=X species. One possibility is that a C—O—H unit will be formed, where the OH unit is called a Hydroxyl Group. When OH is incorporated into a hydrocarbon molecule in place of one of the hydrogen atoms, the new molecule is called an alcohol. Oxygen also forms a C—O—C unit and molecules containing this unit are called ethers. Nitrogen has a valence of 3 and can form three types of species containing at least one C—N bond: R—NH 2, R 2 NH and R 3 N, where “R” represents a carbon group. These nitrogen-containing units are known as amino groups, and a molecule containing an amino group is called an amine. The OH unit, the C—O—C unit, and the amine units are functional groups. These particular functional groups contain polarized covalent bonds (C=X) and their chemical reactions will differ from the C=C and C≡C units discussed above (see Section 1.10.B). The OH unit attached to carbon in methanol is a functional group called a Hydroxyl Group. A carbon molecule containing an OH group (hydroxyl functional group) is called an alcohol. A primary alcohol is characterized by a RCH 2 —OH unit, a secondary alcohol has the OH unit attached to a carbon atom that has one H and two carbon groups (R 2 CH—OH), and a tertiary alcohol has the OH unit attached to a carbon atom that has three carbon groups (R 3 C—OH). In the IUPAC system, alcohols are named using the carbon prefix and the suffix, -ol (taken from the generic name alcoh ol)

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  eBook - ePub

  Understanding Advanced Organic and Analytical Chemistry

  The Learner's ApproachRevised Edition

  • Kim Seng Chan, Jeanne Tan;;;(Authors)
  • 2016(Publication Date)
  • WS EDUCATION

    (Publisher)

  CHAPTER 8

  Alcohols and Phenol

  8.1 Introduction

  Water, H—O—H, is a molecule that is capable of forming hydrogen bonds, and the hydrogen atom is only acidic enough to react with reactive metals, such as sodium, to liberate hydrogen gas. This acid– metal reaction is a characteristic property of an acid, provided the acid is indeed acidic enough to react with the metal. What does it mean? Water is not acidic enough to react with zinc, but hydrochloric acid is. Thus, if one uses zinc metal to determine whether water is an acid or not, then water would fail the acidic test. Other characteristic properties, if they can be observed, include reaction with a carbonate/hydrogencarbonate to give off carbon dioxide gas and reaction with a base to give salt and water. Again, note that an acid may not demonstrate all three characteristics at the same time.

  If one of the hydrogen atoms of the H−O−H molecule is replaced by a sp3 hybridized carbon atom, one would get a homologous group of organic molecules known as alcohol. These compounds have physical and chemical properties similar to that of water. Alcohols, usually abbreviated as ROH, are organic compounds that contain the hydroxyl functional group, which is basically an −OH group bonded to a C atom. They have the general formula Cn H

  2n+1

  OH. The following structure shows the dipoles that are being created in an ethanol molecule due to the more electronegative oxygen atom.

  Q:

  Can we replace both the hydrogen atoms of the H—O—H molecule with carbon atoms?

  A:

  Certainly! We would get a class of compound known as ether, which has the C—O—C functional group. Ether is a functional group isomer of alcohol, and it shares the same molecular formula, Cn H2n+2 O, as alcohol. Notice that the C:H ratio of both the alcohol and ether are same as alkane, Cn H2n+2

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